Patients who received acupuncture experienced a greater reduction in their pain compared with those who received standard pain treatments without acupuncture, and those who received fake acupuncture treatment, called "sham" acupuncture. The benefit of real acupuncture over sham acupuncture was only slight, the researchers said.

The findings suggest that overall, acupuncture is effective, and is a reasonable treatment option for patients with chronic pain, the researchers said.

However, because the difference between real and shame acupuncture was small, it's likely that most of the benefit of acupuncture is indeed due to the placebo effect, the researchers said.

In general, "about a third of the effect of any treatment is a placebo effect," said study researcher Andrew Vickers, of Memorial Sloan-Kettering Cancer Center, in New York City. "In acupuncture, it's more like two-thirds, Vickers said.

Many patients with chronic pain who resort to acupuncture have not responded to standard treatments, or experienced significant side effects from them, Vickers said.

Treating chronic pain

About 3 million Americans receive acupuncture each year, and chronic pain is the most common reason for the therapy, the researchers said. Because researchers have not determined how acupuncture could work to reduce pain, its use is controversial.

In the new study, Vickers and colleagues analyzed information from 17,922 patients who participated in 29 studies conducted in the United States, United Kingdom, Germany, Spain and Sweden. Many previous studies of acupuncture were not rigorously designed, the researchers said, and they excluded these from their analysis.

In the included studies, participants with chronic pain were randomly assigned to receive acupuncture, sham acupuncture or no acupuncture. Their pain was assessed at least four weeks after treatment.

In the sham acupuncture procedures, needles were inserted too shallowly to stimulate an acupuncture point, or using a machine with a tip that causes a prickling sensation, but did not actually push a needle into the skin.

Patients who received acupuncture reported less pain after treatment than those who received no acupuncture or sham acupuncture.

After treatment, the percentage of patients reporting their pain was "much better" was 30 percent for those who received no acupuncture, 42.5 percent for those who received sham acupuncture, and 50 percent for those who received real acupuncture, Vickers said.

Acupuncture vs. placebo

The new study gives "some robust evidence that acupuncture seems to provide modest benefits over usual care for patients with diverse sources of chronic pain," Andrew Avins, a researcher at Kaiser-Permanente in Oakland, Calif., wrote in an editorial accompanying the study.

However, the benefits of acupuncture seem to come primarily from the placebo effect, Avins said, and acupuncture critics will be sure to point this out. After all, drugs are required to perform better than a placebo before they are approved for use, he said.

Still, the performance of a therapy against a placebo is not the only way to measure the treatment's effectiveness, Avins said.

"At the end of the day, our patients seek our help to feel better, and lead longer and more enjoyable lives," Avins said. "Perhaps a more productive strategy at this point would be to provide whatever benefits we can for our patients, while we continue to explore more carefully all mechanisms of healing," Avins said.

The study and the editorial were published online on Sept. 10 in the journal Archives of Internal Medicine.